// datalog

\e 1

\l unify

read:{program@0::[".d"~-2#x;x;x,".d"]}
program:{(clause . parts blanks uncomment@)'x}
query:{:[#x;clause[();x]1;x]}
split:{1_'(&x=y)_ x:y,x}
dlb:{((x=" ")?0)_ x}
dtb:|dlb@|:
deb:{x@&~0&':x=" "}
db:deb dlb dtb@
blanks:{_ssr/[x;"\t\n\r";" "]}
uncomment:{(x?"%")#x}
parts:{2#split[x;":"],,()}
clause:{(*forms x;forms y)}
forms:{:[#x;value'split[x;","];x]}
value:{:["!"=*x;0#`;atom x nest x]}
atom:{:[~4:x;_f'x _dv" ";@x;`$x;`$split[db x;" "]]}

nest:{*{y . x}/[(();,0;0)
                ({(x;@[-1_ y;-2+#y;+;1];z+1)}
                 {(.[x;-1_ y;,;z];@[y;-1+#y;+;1];z+1)}
                 {(.[x;-1_ y;,;,!0];y,0;z+1)})1+-':0,depth x]}

depth:-/+\'"[]"=\:

eval:{[p;q]step[p;q;()]}
step:{[p;q;u]:[#i:&~@:'v:p[;0]unify\:*q;?,/next[p]'[p[i;1],\:1_ q;v[i],\:u];u]}
next:{[p;q;u]:[#q;step[p;apply/[q;u];u];,u]}

if[#_i;p:read _i 0]
eval[p;query"p X Y Z"]